Multilayer structures having annular profiles and methods and apparatus of making the same

ABSTRACT

Disclosed are multilayer film structures having annular profiles, and methods and apparatus of making the structures disclosed. The annular multilayer articles have a uniform thickness, at least four layers and comprise overlapped and non-overlapped circumferential areas; wherein the layer structure of the non-overlapped area is doubled in the overlapped layer. A method of making the structure includes providing a multilayer flow stream with at least four layers of thermoplastic resinous materials; feeding the multilayer flow stream to a distribution manifold of an annular die to form an annular multilayer flow stream; and removing the annular multilayer flow stream from the annular die to form the annular multilayer structure. Also disclosed is an apparatus, comprising: a feedblock, with optional layer multiplier, that provides a multilayer flow stream of at least four layers to the manifold of an annular die; and an annular die having at least one distribution manifold that extrudes a multilayer flow stream.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to multilayer structures, and moreparticularly, to multilayer structures having annular profiles andmethods and apparatus of making the same.

2. Discussion of the Related Art

The current multilayer film processing technologies are referred to ascast film and blown films. Cast film processes use a flat planar type ofproduction process and are suited to produce flat plastic film and sheetthat often have up to about 15% edge trim. Blown film process are knownto provide greater flexibility in film or sheet width changes on thesame line, achieve better economics in lower volume specialtyapplications where frequent product changeover is required and typicallyavoid the yield losses associated with edge trim.

Multilayer films are made by known layering processes typically using auni-axial cast or planar sheet process or lamination. Coextruded castfilm or sheet structures typically have 3 to 5 layers; however, castfilm or sheet structures including hundreds of layers are known. Forexample, early multilayer processes and structures are shown in U.S.Pat. No. 3,565,985; U.S. Pat. No. 3,557,265; and U.S. Pat. No.3,884,606. WO 2008/008875 discloses a related art method of formingmulti-layered structures having many, for example fifty to severalhundred, alternating layers of foam and film. The processes as shown,however, induce only substantially uni-axial orientation, namely, in themachine direction. This is disadvantageous since the resultingstructures may possess unbalanced mechanical properties due to veryunbalanced orientation. Subsequent orientation processes can be used(e.g. tenter-frame process) to achieve bi-axial orientation. Theseadditional processes are elaborate and expensive and the desired degreesof orientation may be different than desired because it occurs withdimensional limitations and at a relatively cooler polymer temperaturebelow the melting point of the highest melting point polymer in themultilayer film.

Multilayer structures having annular profiles with limited numbers oflayers are used in numerous applications. These annularly shaped,tube-like structures include, for example, the “bubbles” in blown filmprocesses, coatings on wires or cables, blow molded articles and theparisons or preforms used in their production, and pipe. Such articlestypically contain 2 to 10 layers and have annular layers supplied byseparate manifolds. Orientation process steps in the extrusion ofannular profiles and products, such as the inflation of a blow moldedarticle or the “bubble” in a blown film process, can very advantageouslybe utilized to provide biaxial orientation (sometime referred to asmulti-axial orientation) that is known to provide polymer resin articleswith very advantageous combinations of physical properties.

As well known in the art, blown film, blow molded and other annularshaped articles may be made by feeding a polymer melt flow into adistribution manifold of an annular die. Obtaining multiple layersgenerally requires a distribution manifold or mandrel to be designed andfabricated for each layer; e.g. a 6 layer annular structure would bemade using a die containing 6 individual distribution manifolds, one foreach layer. The design and fabrication of these multiple distributionmanifolds to produce annular structures with a large numbers of layersis very difficult and limited in the number of annular layers that canbe produced in a structure. See for example a sequential manifoldlayering technique for an annular die, as taught in Dooley, J. and Tung,H., Co-extrusion, Encyclopedia of Polymer Science and Technology, JohnWiley & Sons, Inc., New York (2002).

Another method of making a multilayered structure having an annularprofile includes using a spiral mandrel die. In a spiralmandrel/distribution manifold die, the polymer melt flow fed to thedistribution manifold of the die flows through a manifold channel whichis spirally cut from the entry to near the exit of the manifold, asdescribed in Extrusion Dies, Design and Engineering Computations, WalterMichaeli, 1984, pages 146-147. The flow through the distributionmanifold of the spiral die is not suitable for processing more than asingle layer melt flow in a single distribution manifold since it wouldcause a multi-layered melt flow to become discontinuous and lose layerintegrity.

U.S. Pat. Nos. 3,308,508, 5,762,971 and 6,413,595 disclose forming anannular multilayer structure in a so-called pancake die (also known asplanar geometry). The pancake die includes multiple stacked planar orflat distribution manifolds. Each of several polymer melt flows is fedinto a distribution manifold. The multilayered structure is formed byjoining the several concentric melt flows after each melt flow exits itsdistribution manifold. If a large number of layers are desired, a largenumber of stacked manifolds are required. This can lead to a largepressure drop and extended residence times in the die. U.S. Pat. Nos.5,762,971 and 6,413,595 disclose producing a final multilayer structurehaving a maximum of about 27 layers.

Using a spiral pancake die, multi-layered structures having up to 11layers are known. However, these multi-layered structures are similarlymade by stacking several spiral distribution manifolds on each other toform one annular die and combining the melt flow streams as they areexiting the entire annular die.

Another related art method of making a multilayered structure having anannular profile includes using an annular die, such as that described inU.S. Pat. No. 6,685,872. As disclosed, 3 layers are fed into one singledistribution manifold of the annular die. The disclosed manifold designprovides an annular multilayer structure which has a non-uniformcircumference with a designed overlap section where the layer structureis overlapped in such a way that the overlapped area at least maintainsthe barrier properties of the layer structure in the non-overlappedarea.

US 2008/0157443 describes a method and apparatus for making a parison.The apparatus has a mandrel housing with a side channel substantiallytransverse to the mandrel channel. The mandrel has an axially orientednotch in an exterior surface which is in fluid communication with twofluid channels that extend continuously downwardly around the mandrel tomeet one another on the opposite side of the mandrel from the notch. Theexamples disclose structures having up to 17 layers, although itdiscusses composite streams having up to 100 layers.

However, there is always a need to produce annular multilayeredstructures having a larger number of layers; use a reduced number ofdistribution manifolds in a die; produce annular multilayered structureshaving improved combinations of physical and mechanical properties;and/or reduce the number of processing steps and increase flexibility inannular structure production equipment.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to multilayer structureshaving annular profiles and methods and apparatus of making the samethat substantially obviate one or more problems due to limitations anddisadvantages of the related art. The various embodiments of the presentinvention can provide one or more of the following advantages.

An advantage of the present invention is to provide multilayerstructures having annular profiles and having a high number of layers,which structures may be used to produce articles having a more uniformbi-axial orientation achieved in one step.

Another advantage of the present invention is to provide multilayerstructures having annular profiles and having a larger number of and/orthinner layers than prior annular structures using a reduced number ofdistribution manifolds.

Another advantage of one embodiment of the present invention is toprovide multilayer structures having annular profiles which may be usedto produce blown film or blow molded articles in which the circumferenceof the structure avoids a conventional welding or overlapping area wherestructure properties will be undesirably or adversely affected. It is ofcourse recognized that blown film products are not typically sold orused as annular structures, having been converted from an annularstructure through known process steps to flat sheet products.

Another advantage of an alternative embodiment of the present inventionis to provide multilayer film/foam structures having annular profileshaving cross sections which contain foam layers and allowing downweighting while maintaining an acceptable balance of other physicalproperties.

Another advantage of an alternative embodiment of the present inventionis to provide multilayer film structures having annular profiles havingcross sections which contain inorganic filler layers in controlledquantities allowing tailoring of physical properties.

Another advantage of one embodiment of the present invention is toprovide multilayer structures having annular profiles in which anincrease in the number of layers is achieved while generally maintaininglayer integrity for the majority of the layers.

In another alternative embodiment, another advantage of the presentinvention is to provide multilayer structures having annular profilesthat are cost-effective for various applications and may have, or may beused to provide articles that have, at least one of: reduced density,improved barrier, improved layer uniformity, improved strength, improvedinsulation, improved toughness, improved tear resistance, improvedpuncture resistance, and improved stretch performance.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theadvantages of the invention will be realized and attained by thestructure and method particularly pointed out in the written descriptionand claims hereof as well as the appended figures.

To achieve these advantages and in accordance with the purpose of theinvention, as embodied and broadly described herein, there are providedthe following embodiments and preferred aspects of the presentinvention. One embodiment of the invention is a method of making anannular multilayer structure, comprising: providing a multilayer flowstream with at least four layers of thermoplastic resinous materials;feeding the multilayer flow stream to a distribution manifold of anannular die to form an annular multilayer flow stream; and removing theannular multilayer flow stream from the annular die to form the annularmultilayer structure.

In another embodiment the inventive method comprises providing amultilayer flow stream with at least two layers of thermoplasticresinous materials; encapsulating the multilayer flow stream with atleast one encapsulating layer to form an encapsulated multilayer flowstream having at least four layers of thermoplastic resinous material;feeding the encapsulated multilayer flow stream to a distributionmanifold of an annular die to form an annular multilayer flow stream;and removing the annular multilayer flow stream from the annular die toform the annular multilayer structure. In further alternativeembodiments, the distribution manifold has a cylindrical body, a taperedcylindrical body or a planar body.

In an alternative embodiment, the distribution manifold has a cross-headstyle geometry, wherein the multilayer flow stream is split into atleast two flow streams, wherein two flow streams move in oppositedirections around a circumference of the distribution manifold,preferably in one embodiment wherein the flow streams overlap in an areaon the modified crosshead distribution manifold. In a furtheralternative aspect, the multilayer flow stream is fed into the singledistribution manifold of the annular die through a circular tube flowchannel having an arc shaped flow direction, wherein the arc has aradius of curvature larger than the diameter of the tube.

In accordance with another alternative embodiment of the invention, themethod is further comprising providing at least one additional flowstream to the multilayer flow stream within the annular die using atleast one additional distribution manifold and in such case, theadditional flow stream may optionally be a multilayer flow stream. Otheroptional methods according to the invention further comprise adding afoaming agent or inorganic filler to at least one of the thermoplasticresinous materials before providing the multilayer flow stream.

In yet other alternative embodiment, the method according to theinvention comprises placing the annular multilayer structure in the formof a parison inside a blow molding mold and inflating the annularmultilayer structure to the shape of the mold or drawing the annularmultilayer structure in a molten state to bi-axially orient thestructure; and cooling the structure and optionally including re-heatingthe cooled structure to a temperature below the melting point of thehighest melting point polymer in the structure; drawing the structureuni-axially or bi-axially to orient the structure; and subsequentlycooling the structure. In further optional aspects, the multilayer flowstream includes greater than about 5 layers, and alternatively greaterthan about 25 layers.

In a further alternative aspect, the invention is an annular multilayerarticle having a uniform thickness, at least four layers and comprisingoverlapped and non-overlapped circumferential areas; wherein the layerstructure of the non-overlapped area is doubled in the overlapped layer;with there also being an option that the article is comprising twoexternal skin layers on either side of a microlayer component providingat least 15 layers. In further alternative embodiments, the multilayerblown film comprises a microlayer component having at least 27 layers.

In a further alternative embodiment, the invention is an apparatuscomprising: a feedblock, with optional layer multiplier, that provides amultilayer flow stream of at least four layers to the manifold of anannular die; and an annular die having at least one distributionmanifold that extrudes a multilayer flow stream. Optionally, in theapparatus according to the invention, the annular die manifold is amodified crosshead design splitting the flow stream and providing flowstream overlap area prior to extrusion of the multilayer flow streamand/or has a cylindrical body, a tapered cylindrical body or a planarbody.

In a further alternative embodiment of the apparatus according to theinvention, the apparatus as described above further comprises anencapsulation die between the feedblock (or optional layer multiplier)and the manifold that encapsulates the flow stream prior to entry intothe manifold and/or further comprising an arc-shaped circular tube flowchannel between the encapsulation die and the manifold and wherein aflow stream entry end of the circular tube flow channel is oriented atabout a 90 degree angle with respect to a flow stream exit end of thecircular tube flow channel.

In a preferred alternative embodiment of the present invention, blownmultilayer films and processes according to the invention offergenerally improved properties due to their annular die production,biaxial orientation (versus cast multilayer films) and/or increasednumber of layers. In general, improvements can be obtained in one ormore of the tensile, toughness, stretch and/or barrier properties.Although biaxial orientation can also be obtained with cast films usingtentering, this is an expensive, capital intensive unit operation.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying figures, which are included to provide a furtherunderstanding of the invention and optional embodiments of theinvention, are incorporated in and constitute a part of thisspecification, illustrate embodiments of the invention and together withthe description serve to explain the principles of the invention. In thedrawings:

FIG. 1 is a schematic diagram illustrating a method of making amultilayer blown film for a multilayer film composite structure inaccordance with an embodiment of the present invention; and

FIG. 2 is a schematic diagram illustrating a method of making amultilayer blow molded article from a multilayer film compositestructure in accordance with an embodiment of the present invention.

FIG. 3 is a photograph of a hardened multilayer flow stream from a largeradius circular tube flow channel.

FIG. 4 is a photograph of the cross section of the segment of FIG. 3.

FIG. 5 is an illustration of a die having a large radius circular tubeflow channel.

FIG. 6 is an illustration of a die having a small radius circular tubeflow channel.

FIGS. 7A-B are illustrations of different embodiments of the overlaparea of an annular multilayer structure.

FIGS. 8A-B are atomic force microscope (AFM) photographs of themicrolayers in the overlap and non-overlap areas of an annularmultilayer structure.

FIG. 9 is a (TEM) photograph of the microlayers in an overlap area of anannular multilayer structure.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to embodiments of the presentinvention, examples of which are disclosed in the specification andillustrated in the accompanying figures. It will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the spirit or scope ofthe invention. Thus, it is intended that the present invention cover themodifications and variations of this invention provided they come withinthe scope of the appended claims and their equivalents.

The numerical ranges in this disclosure include all values from andincluding the lower and the upper values, in increments of one unit,provided that there is a separation of at least two units between anylower value and any higher value. As an example, if a compositional,physical or other property, such as, for example, thickness and densityreduction, etc., is greater than 10, it is intended that all individualvalues, such as 10, 11, 12, etc., and sub ranges, such as 100 to 144,155 to 170, 197 to 200, etc., are expressly enumerated. For rangescontaining values which are less than one or containing fractionalnumbers greater than one (e.g., 1.1, 1.5, etc.), one unit is consideredto be 0.0001, 0.001, 0.01 or 0.1, as appropriate. For ranges containingsingle digit numbers less than ten (e.g., 1 to 5), one unit is typicallyconsidered to be 0.1. These are only examples of what is specificallyintended, and all possible combinations of numerical values between thelowest value and the highest value enumerated are to be considered to beexpressly stated in this disclosure.

The method of making an annular multilayer structure in accordance withthe present invention and as herein described below includes obtainingand utilizing a multilayer flow stream which is typically provided froma multilayer coextrusion process step, and optionally may be providedfrom a further layer multiplication process step. The claimed methodoptionally includes an encapsulation process step. The claimed methodincludes providing a multilayer flow stream with at least four layers ofthermoplastic resinous materials to a distribution manifold in anannular die process step. Optionally, blown film process steps or blowmolding process steps may be performed upon receiving the multilayerflow stream from the annular die exit.

Multilayer Flow Stream

As used herein, the term “flow stream” or “melt stream” with referenceto a thermoplastic resinous material refers to the material, typically apolymer or polymeric material as described further below, being heatplastified (heated to a temperature at or above the melting or glasstransition temperature of the material, i.e. a temperature where thematerial becomes sufficiently liquid like to flow in the equipmentreferred to in this embodiment), thermoplastically processable andflowable under sufficient pressure conditions. A flow stream can beprovided by a number of known processing techniques. Preferably, a flowstream is provided from an extruder (i.e., by extrusion) optionallyincluding a gear pump for flow uniformity, but it can also be providedas output from other heat plastification process steps using a gearpump. A multilayer flow stream with layers of thermoplastic resinousmaterials can be provided from two or more flow streams by knownlayering techniques including primarily well known coextrusion processesand, optionally, also by known layer multiplication techniques asdiscussed in further detail below.

The multiple streams of thermoplastic resinous material may becoextruded through the use of known feedblock technology with two ormore orifices arranged so that the resulting extrudate streams merge andweld together into a multilayer flow stream and continue through a flowchannel toward the annular die. The multilayer flow stream may be, forexample, a generally flat rectangular laminar stream, i.e., generallyflat planar layers of about the same thickness and width as taught in WO2008/008875; U.S. Pat. No. 3,565,985; U.S. Pat. No. 3,557,265; and U.S.Pat. No. 3,884,606, all of which are hereby incorporated by referenceherein. Alternatively, 2 or more layers of the multilayer flow streamcan be provided by encapsulation techniques such as shown by FIGS. 2 and5 of U.S. Pat. No. 4,842,791 encapsulating with one or more generallycircular or rectangular encapsulating layers stacked around a core or asshown by FIG. 8 of U.S. Pat. No. 6,685,872 with a generally circular,nonuniform encapsulating layer. As can be envisioned, an encapsulatinglayer has the effect of providing 2 outside layers to a multilayer flowstream when the flow stream is provided to and exits the annular die.U.S. Pat. No. 4,842,791 and U.S. Pat. No. 6,685,872 are herebyincorporated by reference herein.

In the present invention, a coextrusion process for providing amultilayer flow stream includes combining simultaneously or sequentiallyat least a first melt stream of thermoplastic resinous material and atleast a second melt stream of thermoplastic resinous material andoptionally additional streams. In simultaneous layering, the layers maybe added or combined at the same point of the flow stream. Simultaneouslayering may be performed, if, for example, the rheologies of theresinous materials are similar. In a sequential layering feedblock, theadditional layers are added at different points along the flow stream.For example, the multilayer streams may be provided in a simultaneouscombination of the streams by the feedblock processes as taught in U.S.Pat. No. 3,565,985; U.S. Pat. No. 3,557,265; and U.S. Pat. No.3,884,606. As taught in U.S. Pat. No. 3,557,265 and U.S. Pat. No.3,884,606, their multilayer flow streams are also referred to as“interdigitated” or “interleaved.”

A form of sequential stream addition is shown in U.S. Pat. No. 4,842,791and U.S. Pat. No. 6,685,872, both of which are hereby incorporated byreference herein, where multilayer streams are provided by encapsulatingan initial stream.

In one embodiment of the invention, as shown in FIG. 1, materials fromsingle-screw extruders 1 and 5 are fed into a two layer A/B feedblockdie 6 having at least two orifices. In another embodiment of theinvention, as shown in FIG. 2, materials from single-screw extruders 1and 2 are fed into a two layer A/B feedblock die 4 having at least twoorifices.

Optional Layer Multiplication

Optionally, after the feedblock coextrusion process or an initialmultilayer flow stream is otherwise provided, the multilayer flow streammay then be subjected to further layer multiplication process steps asare generally known in the art. See for example, U.S. Pat. No. 5,094,788and U.S. Pat. No. 5,094,793, hereby incorporated herein by reference,teaching the formation of a multilayer flow stream by dividing amultilayer flow stream containing the thermoplastic resinous materialsinto first, second, and optionally other substreams, and combining themultiple substreams in a stacking fashion and compressing, therebyforming a multilayer flow stream. The multiple stacked substreams arefused to each other in an adjacent and a generally parallel relationshipwith one another in the multilayer flow stream. Within the multilayerflow stream, the multiple substreams exhibit uniformity, continuity, andthickness specifically calculated to provide a desired configurationhaving desired properties. The layer multiplication process may yieldmultilayer flow streams that contain many layers, such as severalhundred layers.

For the multilayer flow streams used in the present invention, dependingon factors such as desired properties, costs of manufacture, end use,etc., the streams contain at least 4 layers, preferably greater thanabout 4 layers, preferably greater than about 5 layers, preferablygreater than about 8 layers, preferably greater than about 10 layers,preferably greater than about 11 layers, more preferably greater thanabout 20, more preferably greater than about 25, more preferably greaterthan about 27 layers, more preferably greater than about 30 layers, orgreater than about 40 layers, or greater than about 50 layers, orgreater than about 60 layers, or greater than about 70 layers, orgreater than about 75 layers, or greater than about 80 layers, orgreater than about 90 layers. Also, although the number of layers in thestreams may be essentially limitless, the streams may be optimized tocontain up to and including about 10,000 layers, preferably up to andincluding about 1,000 layers, more preferably up to and including about500 layers, or up to and including about 400 layers, or up to andincluding about 300 layers, or up to and including about 250 layers, orup to and including about 200 layers, or up to and including about 175layers, or up to and including about 150 layers, or up to and includingabout 125 layers, or up to and including about 100 layers. As known inthe art, multilayer structures containing large numbers of layers asprovided in one or more of the methods discussed above are oftenreferred to as “microlayer” structures.

In one embodiment of the invention, as shown in FIG. 1, materialsexiting the feedblock die 6 are fed into a series of optional layermultipliers 7. In another embodiment of the invention, as shown in FIG.2, materials exiting the feedblock die 4 are fed into a series ofoptional layer multipliers 5.

Optional Encapsulation

Optionally, if not already employed to provide at least two of thelayers in the multilayer flow stream, encapsulation may then be employedby known methods as mentioned above to provide surface layers thatprotect an interior layer structure such as the very thin layers thatare provided in a microlayer structure. See for example U.S. Pat. No.5,269,995, which is hereby incorporated by reference herein. Forexample, in the present invention, the encapsulation die as shown inFIG. 4 and as described with reference to FIGS. 4, 5, 7 and 8 asdisclosed in U.S. Pat. No. 6,685,872, herewith incorporated herein byreference, may be employed. Encapsulation with a relatively uniformencapsulating layer can also be provided according to the teachings ofU.S. Pat. No. 4,842,791, incorporated by reference herein. As describedin U.S. Pat. No. 6,685,872, a non-uniform encapsulating layer can beemployed, especially if needed to provide the desired overlapping areausing a modified crosshead annular die of the type shown therein. Astaught therein, a non-uniform die gap can provide an appropriatethickness variation in the encapsulating layer. For example, in oneembodiment of the invention the entire circumference or periphery of themultilayer flow stream may be encapsulated. For example, the ends of themultilayer composite stream may be fully encapsulated. If, for example,the multilayer flow stream includes two layers and is then encapsulated,the cross-section of encapsulated multilayer flow stream shows fourlayers.

Encapsulation layer(s) may advantageously improve the flow stability ofthe multilayer flow stream as it flows through the encapsulation die,the annular die, and any subsequent operations, such as shown with theencapsulation die described in U.S. Pat. No. 6,685,872. Theencapsulation layer(s) may also have a functional purpose, for example,to improve weathering, UV stability, etc. In an alternative embodimentof the invention, the optional encapsulation layer effect mayalternatively be provided for less than the entire circumference orperiphery of the multilayer flow stream, including by the use ofprotective surface layers or a number of feedblock layers in excess ofthe number needed for obtaining the basic, desired annular structureproperties. The encapsulation layer(s), for example, may be sacrificiallayers that may be subsequently removed or damaged. As shown in FIG. 1,at least one encapsulation layer is incorporated onto the multilayercomposite stream using optional extruder 3 in the optional encapsulationdie 8. As shown in FIG. 2, optional encapsulation layers areincorporated onto the multilayer composite stream using optionalextruder 3 in the optional encapsulation die 6.

Alternatively, only a portion of the circumference of the multilayerflow stream can be encapsulated, if desired. For example, the top andbottom of the stream can be coated with a layer, while leaving the sidesexposed.

Optional Flow Channel

Optionally, in some alternative embodiments of the invention, after theformation of a generally rectangular or other non-circular multilayerstream, the stream has a relatively long distance to travel (forexample, greater than about 5 to 10 times the flow diameter) or the flowdirection needs to be changed (for example, from a horizontal extrusionplane to vertical blown film process steps). In such cases, a circulartube flow channel may be provided for the encapsulated multilayer flowstream to enter. The cross-sectional shape of the non-circular flowstream smoothly transitions to a circular shape which, when maintainedin the flow stream, minimizes layer distortion that may be caused bysecondary flows produced by elastic forces in the multilayer flowstream. If used, this circular tube flow channel may be formed into anarc with a relatively large radius of curvature relative to the tubediameter in order to change the flow direction of the multilayer flowstream, from horizontal to vertical, for example. The flow direction ofthe discharging end of the circular tube flow channel may be oriented atan angle of up to 90 degrees or greater with respect to the flowdirection entering the circular tube flow channel. For changing the flowdirection of the circular tube flow channel about 90 degrees, the ratioof the radius of the circular tube flow channel curvature (providing thechange in flow direction) to the circular tube flow channel innerdiameter is preferably greater than 1 to 1, preferably greater than 2 to1, more preferably greater than 3 to 1, and more preferably greater than5 to 1. The multilayer flow stream should be maintained in the circulartube cross section until it approaches the distribution manifold channelof an annular die, at which time the multilayer flow stream can smoothlytransition from a circular geometry to an appropriate geometry for thedistribution manifold channel of the annular die.

FIG. 3 shows a sample of a multilayer flow stream from a circular tubeflow channel having a large radius of curvature relative to the tubediameter. The radius of curvature of the circular tube flow channel was3.4, the inner diameter of the circular flow tube channel was 1.0, andthe ratio of the two was 3.4. The multilayer flow stream included 27alternating layers of polystyrene colored black and white for contrast.It was made using two 1.25 in. extruders running at 420° F. and a rateof 12 lb/hr. The process details and equipment are described below underProcedure. The extruders were stopped, and the multilayer flow streamwas allowed to cool and harden in the circular flow tube channel. Thecircular flow tube channel was then removed, leaving the hardenedmultilayer material. The direction of flow was toward the positionlabeled 4 on the bottom right side.

The cross-sectional area of 4 was photographed as shown in FIG. 4 (whichis after the transition from the circular geometry of the circular tubeflow channel to a square geometry). FIG. 4 shows that the layersremained intact as they flowed around the curve toward the positionlabeled 4.

FIG. 5 shows a portion of a crosshead die 100. In a crosshead die, theflow direction must be changed from the horizontal extruder plane to thevertical die plane. The multilayer flow stream flows into the die intube 105. It enters the die 100 through the circular flow tube channel110 having a relatively large radius of curvature relative to the tubediameter. The flow is turned 90° from the incoming horizontal tovertically upward. The flow enters channel 115 leading around the die tothe overlap area on the opposite side. The material flows upward fromchannel 115 through channel 120 and out of the die. One of skill in theart will recognize that the flow in the die could be up or downdepending on the particular type of die.

FIG. 6 shows a portion of a crosshead die 200 in which the radius ofcurvature is small. The flow stream enters the die from tube 205. Thecircular flow tube channel 210 has a small radius of curvature relativeto the tube diameter, for example less than 1 to 1). The flow directionis turned 90° from horizontal to vertical. The flow enters channel 215around the die, and upward from channel 215 through channel 220 and outthe die.

The circular flow tube channel can be inside the die, as shown in FIG.5, or outside of the die. If it is outside of the die, the flow tubechannel changes the flow from horizontal to vertical before it entersthe die, and the flow in the die is vertical to the channels around thedie.

Therefore, as described above, the multilayer flow stream can beprovided from a variety of different sources or steps including one ormore of: a feedblock, an optional layer multiplier(s), an optionalencapsulation die, or an optional circular tube flow channel.

Annular Die Process

The multilayer flow stream is provided to the annular die by being fedor delivered into a single distribution manifold of an annular die toform an annular multilayer flow stream by the time it exits the annulardie. The distribution manifold distributes the multilayer flow stream toform an annular shape while maintaining the multilayer flow stream layercontinuity. The single distribution manifold may have for example, acylindrical body shape, a tapered cylindrical body shape or a planarbody shape, all feeding to and exiting out the annular die.

More than one multilayer flow stream can be supplied to the annular die,but each multilayer flow stream has its own distribution manifold. Forexample, in FIG. 1, extruder 2 (or extruder 4, or both) could bereplaced by an arrangement of one or more of extruders, feedblocks,layer multipliers, and encapsulation dies to obtain a second (or third)multilayer feed stream flowing into distribution manifold 11 (ordistribution manifold 9).

It should be noted that in typical industry usage, the term “mandrel”often refers to or includes a “distribution manifold” and is usedsomewhat interchangeably with that term. As used herein relating to anannular die, the distribution manifold is the flow space or flow channelarea that receives and transitions a flow stream over and around thesurface of a generally cylindrical, planar or tapered cylindrical shapedmandrel unit that creates the annular profile flow stream that exits theannular. It is often created by and located between a center mandrelunit and an outer or upper shell or plate unit. The manifold distributesa polymer melt flow around the mandrel and forms the flow into theannular shape for the exit of the die.

If, for example, the manifold has a planar body, it lies between twohorizontally oriented plate-type units and leads to a verticallyoriented annular die. In this situation, the manifold will be orientedin a direction generally parallel and coplanar to the flow direction andlayer interfaces within the multilayer flow stream. Advantageously, theplanar manifold distributes and forms a multilayer flow stream into theannular shape for the exit of the die.

In one embodiment, the single distribution manifold may have across-head style geometry. In a distribution manifold having across-head style geometry, as shown for example in FIG. 9 of U.S. Pat.No. 6,685,872, an entering polymer melt flow stream splits at or nearthe entrance of the manifold into two flow streams that travel ingenerally opposing circumferential directions around a mandrel and alsoprovides a very thin flow stream that flows toward the die exit alongthe mandrel in the axial direction. The split polymer melt flow streamsthen continue around the manifold in opposing directions to meet or joinflows at or near the opposite side of the mandrel and form a generallyannular flow stream that travels toward the annular die exit. In somecrosshead-type annular dies, depending upon the die construction and/ormaterial selection there may be a noticeable weld line at the joint orseam where the two flows meet. This may be undesirable is someapplications and might possibly be advantageous in other applications.

In an alternative embodiment of the present invention, the singledistribution manifold has a modified cross-head style geometry. Themodified cross-head style geometry of the distribution manifold isdescribed and shown in FIGS. 9, 10, 11, and 12 of U.S. Pat. No.6,685,872, herewith incorporated by reference. This distributionmanifold having the modified cross-head style geometry includes a bodyand a pair of manifold channels extending from an inlet of thedistribution manifold around the body of the mandrel in opposingdirections. Opposite ends of the manifold channels overlap each otherand greatly diminish the appearance and effect of the weld line.

In a preferred modified cross-head annular die embodiment, themultilayer flow stream may split into at least two split flow streams,wherein each split flow stream travels in opposite directions in thepair of manifold channels around a circumference of the body of thedistribution manifold. In another preferred embodiment, the split flowstreams overlap each other but remain separated on an area on thedistribution manifold where the opposite ends of the manifold channelsoverlap each other. Preferably, the overlap distance is optimized forthe multilayer structure to provide desired article properties in theoverlapped area.

As used herein, the terminology “desired article properties in theoverlapped area” refers to several possible effects that may be providedby the modified crosshead die. For example, the overlapping manifoldareas can be designed to provide generally consistent propertiescircumferentially around the annular structure, extending from thenon-overlapped area into and through the overlapped area. For example,U.S. Pat. No. 6,685,872 discloses maintaining consistent barrierproperties using this technique. Alternatively, since the overlappedarea will have twice the number of layers with half the average layerthickness, it may intentionally exhibit a noticeable transition in termsof physical or optical properties. Having the noticeable transitioncould possibly be advantageously utilized in a number of ways in theannular structure. For example, it might be utilized to enable theconsistent orientation or location of an annular article. It mightprovide an easy way to locate the overlapped area for removal if it isdetrimental to the balance of the article circumference.

With a planar die (“pancake” die), the overlap can be formed by placingone end above the other so the two ends are at different heights (ratherthan at different radial distances as with the modified crosshead die).

The overlap can be formed in a variety of ways, including, but notlimited to, a step change or a sloped change, as shown in FIGS. 7A-B. Itwas surprisingly found that the layers remained intact in the overlaparea, whether formed by the step change or the slope change. This isdemonstrated in FIGS. 8A-B and 9A-B. FIGS. 8A-B are AFM images ofmicrolayers in a blown film. The film had 27 microlayers of alternatinglow density polyethylene and Affinity™ polyolefin plastomer in the core.The film was made using a 1.25 in. and a 1.75 in. extruder running at a50%/50% layer ratio. The core rate was about 12 lb/hr out of a totalline rate of about 60 lb/hr. The process details and equipment aredescribed below under Procedure. FIG. 8A shows the presence of intactmicrolayers in a blown film outside of the overlap area. FIG. 8B showsthe overlap area for the film of FIG. 8A, which has twice as many layersin the same overall film thickness, and the layers remain intact.

FIG. 9 shows a TEM image of the microlayers in the overlap area of ablown film. Sections A and B each contain 100 microlayers of alternatinglow density polyethylene and Affinity™ polyolefin plastomer in the core.The film was made using a 1.25 in. and a 1.75 in. extruder running at a50%/50% layer ratio. The core rate was about 12 lb/hr out of a totalline rate of about 60 lb/hr. The process details and equipment aredescribed below under Procedure. The layers are intact.

It should be noted that the barrier layers in the structures describedin U.S. Pat. No. 6,685,872 are much thicker than the microlayersdescribed here. It is easier to manipulate and maintain a few thickerlayers intact compared to many thinner layers. In addition, it is easierto manipulate layers in a blow molding die which is smaller than atypical blown film die.

As shown in FIG. 1, the optionally encapsulated multilayer flow streamis fed into the distribution manifold 10 of an annular die. Optionally,additional flow streams may be produced by two extruders 2 and 4 and maybe applied to the encapsulated multilayer flow stream by additionaldistribution manifolds 9 and 11 within the annular die. The additionalflow streams may each be single layer or multilayer flow streams,including multilayer flow streams the same as or different from theprimary encapsulated multilayer flow stream. Each of the distributionmanifolds 9 and 11 may be a conventional manifold or may have the samemodified cross-head style geometry of distribution manifold 10.

Then, the annular multilayer flow stream exits, i.e., is removed, fromthe annular die to form the annular multilayered structure.

The overlap of the split flow streams forms a flow stream where the endsof the flow stream are not exposed to the surface of a resultingstructure. In one embodiment, by encapsulating and overlapping themultilayer flow stream, the occurrence of layered ends at the surface ofthe resulting annular multilayer structure may be eliminated and aconventional weld line is eliminated. The elimination of the layeredends and/or weld line beneficially improves both the mechanical andphysical properties of the resulting annular multilayer structure. In atleast one embodiment, the elimination of the layered ends beneficiallyimproves the properties of the annular multilayer structure bymaintaining at least consistent or improved properties in the overlapregion as compared to the properties for the remaining circumference ofthe annular article.

Blown Film and/or Blow Molded Processes

After emerging from the annular die, the annular multilayer structuremay be drawn while in the molten state or in a semi-solid state touni-axially, bi-axially, or multi axially orient the structure. Forexample, inflation into a mold producing radial orientation, axialorientation, and different thicknesses may be referred to multi-axialorientation. Also, for example, uni-axial orientation may be employed toform wire and cable coatings, pipes, tubes, etc. In embodiments where anexpanded thermoplastic resinous material is used, drawing achievesmacroscopic cellular orientation of foamed cells within the expandedthermoplastic resinous material. The foamed cells may have differentdegrees of macro-cellular orientation.

Examples of drawing include, but are not limited to, (i) uni-axialdrawing between an annular die and a drawing roll, (ii) threedimensional inflation, either for free surface blown film bubbleblowing, or parison inflation into a mold (blow molding), and (iii)drawing a profile through a calibrator and/or quench tank. Typicaldrawing ratios, based on a uni-axial drawing process, range from about2:1 to about 50:1, preferably from about 5:1 to about 30:1. Uniaxial“drawing ratios” are the ratio of the drawing speed to the speed atwhich the annular structure is exiting the die. Blow-up ratios, forbi-axial drawing processes, range from about 1.5:1 to 20:1, preferablyfrom about 2:1 to 5:1. A blow-up ratio is the ratio of the diameter ofthe final annular product or article to the diameter of the articleexiting the annular die. Then, the annular multilayer structure isstabilized by cooling, either assisted (e.g., air cooling, quenching,etc.) or unassisted, i.e., equilibrating to ambient room temperature.

As shown in FIG. 1, in one embodiment a blown film bubble 12 may beformed.

As shown in FIG. 2, in forming a blow molded article, the annularmultilayer structure, a parison, may be placed in a blow molding moldand inflated to the shape of the mold to form an annular blow moldedpart. Exemplary blow molded articles may be formed using a typical blowmolding head 7 and mold cavity 8. Blow-up ratios for blow-moldedarticles and blow molding processes range from about 2:1 to 10:1,preferably from about 3:1 to 5:1.

Optionally, a re-heating process may be performed on the annularmultilayer structure. The structure is re-heated to a temperature belowthe melting point of the highest melting point polymer in the structure.Then, the structure is uni-axially or bi-axially drawn in a semi-moltenstate to orient the structure and subsequently cooled. The cooledstructure may be used in, for example, shrink films.

Resulting Annular Multilayer Structure

The annular multilayer structure of the present invention, depending onfactors such as desired properties, costs of manufacture, end use, etc.,may contain, for example, at least about four layers, preferably greaterthan about 4 layers, preferably greater than about 5 layers, preferablygreater than about 8 layers, preferably greater than about 10 layers,preferably greater than about 11 layers, more preferably greater thanabout 20, more preferably greater than about 25, more preferably greaterthan about 27 layers, more preferably greater than about 30 layers, orgreater than about 40 layers, or greater than about 50 layers, orgreater than about 60 layers, or greater than about 70 layers, orgreater than about 75 layers, or greater than about 80 layers, orgreater than about 90 layers. It should be recognized that in certainembodiments, in overlapping areas on the structure, the number of layersmay be twice the number in other areas on the structure. Also, althoughthe number of layers is theoretically nearly limitless, the streams maybe optimized to contain up to and including about 10,000 layers,preferably up to and including about 1,000 layers, more preferably up toand including about 500 layers, or up to and including about 400 layers,or up to and including about 300 layers, or up to and including about250 layers, or up to and including about 200 layers, or up to andincluding about 175 layers, or up to and including about 150 layers, orup to and including about 125 layers, or up to and including about 100layers. As known in the art, multilayer structures containing largenumbers of thin layers as provided in one or more of the methodsdiscussed above are often referred to as “microlayer” structures.

In one embodiment of the invention, the resulting annular multilayerarticles have a generally uniform thickness and comprise overlapped andnon-overlapped circumferential areas; wherein the layer structure of thenon-overlapped area is doubled in the overlapped area. As mentionedabove, in certain embodiments where a modified crosshead die provides anoverlapping area, in the overlapping areas on the structure, the numberof layers may be twice the number in other areas on the structure.

As used herein, the term “generally uniform thickness” with reference tothe annular circumference refers primarily to the fact that, in theembodiment where the annular multilayer articles have an overlappingarea, the thickness of the overlapping area can be, is usually intendedto be, and typically is, substantially the same thickness as thenon-overlapped area. This is, of course, subject to minor, occasionaland unintentional thickness differences. General thickness uniformitytherefore means that preferably the structure thickness variation aroundthe annular circumference, particularly between any overlapping andnon-overlapping areas, if any, is generally less than 10%, preferablyless than 5%, more preferably less than 2% most preferably less than 1%.In other embodiments of the invention, the die may intentionally providea somewhat non-uniform thickness in the circumference of the annularstructure.

As apparent from the general description of the invention here and inother sections, the invention provides the benefit of multiple annularlayers and particularly annular microlayers in annular structures wherethe benefit of the multiple layers are provided and maintained aroundthe circumference of the annular article. As discussed above, insituations where an overlapped area is provided, there can be areaswhere the layers themselves are not completely annularly continuous but,instead, have sufficient layer overlapping and/or redundancy tocompensate for the layer thinness and ending point in the overlappingarea. For example, the overlapping areas can be designed to providegenerally consistent properties circumferentially around the annularstructure, extending from the non-overlapped area into and through theoverlapped area.

As known in the practice of multi-layering and microlayering, theaverage layer thickness is a function of, and can be calculated from,the final thickness of the micro/multi-layered structure ormicro/multi-layer component in a structure and the number of layersobtained in that thickness. The preferred thicknesses formicro/multi-layer structures or for use as components in structuresvaries for different specific applications and will be discussed furtherbelow. The annular multilayer structure may be formed in a layeredorganization with a wide variety of repeating layer units or repeatingpatterns, such as repeating A/A, A/B, A/B/A, A/B/C, A/B/C/B/A, etc., bythe selection and use of the appropriate multilayer feed stream andlayer multiplier techniques according to various aspects and embodimentsof the present invention. The thickness of the structure may varydepending on various factors, such as the thermoplastic resinousmaterials used, whether the materials are expanded or non-expanded, thedesired properties of the structure, etc. Also, it should be noted thatdepending upon whether it is subsequently combined with additionallayers from a multilayer annular die, the multi-/micro-layer structurecan form all or part of the film structure. In optional alternativeembodiments of the present invention, the annular multilayer structuresaccording to the present invention are, in effect, a component of themain structure and are combined with additional layers through one ormore additional die manifolds.

In one embodiment of the present invention where the multilayer annularstructure is employed as all or part of a non-expanded film application,preferably a blown annular film structure, the structure would have athickness of at least about 7 micrometers (0.3 mils), preferably atleast about 10 micrometers (0.4 mils), more preferably at least about 15micrometers (0.6 mils). For film applications, the film thickness istypically less than about 380 micrometers (15 mils), more preferablyless than about 250 micrometers (10 mils), and more preferably less thanabout 125 micrometers (5 mil).

The use of the structures for other types of articles, such asblow-moldable parisons, extruded annular profile articles, e.g., pipe,particularly where expanded layers may be employed, may requirethicknesses of at least about 1 millimeter (mm), preferably at leastabout 1.6 mm, and for pipe, up to as thick as about 152 millimeters (6inch), preferably up to and including about 90 mm (3.5 inch). Forblow-molded articles themselves, the wall thicknesses would be in therange of from about 1 mm to about 13 mm.

Optionally, provided either on the surface(s) of the annular multilayerstructure (using additional annular die manifolds) or included in theannular multilayer structures as described above, there can be anexternal “skin”. This can be, for example, one or more coextrudedannular cap layers added to, or excess multiple external skin layersincluded on, one or both opposing sides of the annular multilayerstructure. If present, the external skin layer(s) may comprise greaterthan zero and up to about 90% of a final product structure by thickness,or up to about 80% by thickness, or up to about 70% by thickness, or upto about 60% by thickness, or up to about 50% by thickness, or up toabout 45 percent, or up to about 40 percent, or up to about 30% bythickness based on the total thickness of the structure. If used, anexternal skin would generally comprise at least about 1% by thickness,or at least about 5% by thickness, or at least about 10%, or at leastabout 20%, or at least about 30 percent, or at least about 40%, or atleast about 45%, or at least about 50 percent, or at least about 60%, orat least about 70%, or at least about 75 percent, or at least about 80%by thickness.

Materials for Resinous Layers (and Optional Expanded Layers)

The layers in the multilayer structure can be made of the same materialor two or more different materials.

Any thermoplastic resinous material which can be provided as athermoplastic resinous flow stream and formed into a film may beemployed as a flow stream in the process according to the presentinvention and as a layer in an article according to the presentinvention. Their selection will be determined by the intended use forthe articles as well as any adhesion and/or processing requirements forother layer or flow stream selections. Preferred thermoplastic resinousmaterials include thermoplastic polymers. As used herein “polymer” meansa polymeric compound prepared by polymerizing monomers, whether of thesame or a different type. The generic term “polymer” embraces the terms“homopolymer,” “copolymer,” and “terpolymer,” as well as “interpolymer.”

“Interpolymer” means a polymer prepared by the polymerization of atleast two different types of monomers. The generic term “interpolymer”includes the term “copolymer” (which is usually employed to refer to apolymer prepared from two different monomers), as well as the term“terpolymer” (which is usually employed to refer to a polymer preparedfrom three different types of monomers).

For example, thermoplastic polyolefin polymers, also referred to aspolyolefins may be employed and are well-suited for the practice of theinvention. “Polyolefin polymer” means a thermoplastic polymer derivedfrom one or more olefins. The polyolefin polymer can bear one or moresubstituents, e.g., a functional group such as a carbonyl, sulfide, etc.For purposes of this invention, “olefins” include aliphatic andalicyclic compounds having one or more double bonds. Representativeolefins include ethylene, propylene, 1-butene, 1-hexene, 1-octene,4-methyl-1-pentene, butadiene, cyclohexene, dicyclopentadiene, and thelike. These include, but are not limited to, polyethylene (PE),polypropylene (PP) and polybutylene (PB), and polyvinylchloride (PVC,both rigid and flexible).

Specific examples of useful olefinic polymers include ultra-low densitypolyethylene (ULDPE, e.g., ATTANE™ ethylene/1-octene polyethylene madeby The Dow Chemical Company (“Dow”) with a typical density between about0.900 and 0.915 and a typical melt index (I₂) between about 0.5 and 10),linear low density polyethylene (LLDPE, e.g., DOWLEX™ ethylene/1-octenepolyethylene made by Dow with a typical density between about 0.915 and0.940 and a typical I₂ between about 0.5 and 30), homogeneouslybranched, linear ethylene/alpha-olefin copolymers (e.g., TAFMER®polymers by Mitsui Chemicals America, Inc. and EXAC™ polymers byExxonMobil Chemical (ExxonMobil)), homogeneously branched, substantiallylinear ethylene/alpha-olefin polymers (e.g., AFFINITY™ and ENGAGE™polymers made by Dow and described in U.S. Pat. Nos. 5,272,236,5,278,272 and 5,380,810), catalytic linear statistical olefin copolymers(e.g., INFUSE™ polyethylene/olefin block polymers, particularlypolyethylene/alpha-olefin block polymers and especiallypolyethylene/1-octene block polymers, made by Dow and described in WO2005/090425, 2005/090426 and 2005/090427), and high pressure, freeradical polymerized ethylene copolymers such as ethylene/vinyl acetate(EVA) and ethylene/acrylate and ethylene/methacrylate polymers (e.g.,ELVAX® and ELVALOY® polymers, respectively, by E. I. Du Pont du Nemours& Co. (Du Pont)) and ethylene/acrylic and ethylene/methacrylic acid(e.g., PRIMACOR™ EAA polymers by Dow and NUCREL EMAA polymers by DuPont), various polypropylene resins (e.g., INSPIRE® and VERSIFY®polypropylene resins made by Dow, VISTAMAXX® polypropylene resins madeby ExxonMobil, and random copolymer polypropylene (“RCP”)) and thecycloolefin or cyclic olefin polymers and copolymers (“COP's” and“COC's” respectively, COC's including for example Topas® brand polymersfrom Topas Advanced Polymers and COP's including for example, Zeonex®brand polymers from Zeon Chemicals). COP's and COC's are known anddescribed, for example, in EP-A-0 407 870, EP-A-0 485 893, EP-A-0 503422, and DE-A-40 36 264, incorporated herein by reference. As known, theCOP and COC resins used are composed of one or more cycloolefins suchas, for example, norbornene.

In an alternative embodiment of the present invention, one or more layerin the multilayer flow stream and in the annular multilayer structure isan LLDPE. Preferred LLDPE polymers are ethylene interpolymers ofethylene with at least one C₃-C₂₀ α-olefin. LLDPE copolymers of ethyleneand a C₃-C₁₂ α-olefin are especially preferred. Examples of suchcomonomers include C₃-C₂₀ α-olefins such as propylene, isobutylene,1-butene, 1-hexene, 1-pentene, 4-methyl-1-pentene, 1-heptene, 1-octene,1-nonene, 1-decene, and the like. Preferred comonomers includepropylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene,and 1-octene, and 1-octene is especially preferred.

Other suitable thermoplastic resinous materials include themonovinylidene aromatic polymers which are prepared from one or moremonovinylidene aromatic monomer. Representative monovinylidene aromaticmonomers include styrene, toluene, α-methylstyrene, and the like. Themonovinylidene aromatic polymer can bear one or more substituents, e.g.,a functional group such as a carbonyl, sulfide, etc. Examples ofmonovinylidene aromatic polymers suitable for use as one or more layerin the multilayer flow stream and in the annular multilayer structure isof this invention include polystyrene, polystyrene-acrylonitrile (SAN),rubber-modified polystyrene acrylonitrile (ABS), and rubber-modifiedpolystyrene (HIPS).

Other thermoplastic resinous materials suitable for use as one or morelayer in the multilayer flow stream and in the annular multilayerstructure of this invention include polyesters such as polyethyleneterephthalate and polybutylene terephthalate; polycarbonate resins;poly-lactic acid; polyamides such as the nylon resins including nylon 6,nylon 66 and nylon MXD6; thermoplastic polyurethanes; ethylcellulose;poly(vinylchloride)-vinylidene chloride (PVDC); polyethylene vinylalcohol (EVOH); methyl acrylate-vinylidene chloride copolymer;polymethylmethacrylate; and the like.

Preferably, the thermoplastic resinous materials for these layers arechosen to exhibit optimal properties in the resulting annular multilayerstructure for the given application. In preferred embodiments, materialsare selected based on properties desired in the final resultingstructure. For example, if shrink properties are desired, materialsyielding appropriate shrink properties, such as layers of polyolefinresins, may be selected. If barrier properties are desired, materialsyielding appropriate barrier properties may be selected, such as PVDC orEVOH. If adhesive properties are desired, materials yielding appropriateadhesive bonding behavior between the other layers are chosen, such asEVA and EAA. For example, polyethylene resins having different densitiesmay be employed to optimize stiffness and toughness. Desired propertiesin a final product may affect the choices for the materials for themultilayer structure. The materials may be chosen such that the rheologyof the materials used complement and function with each other.

Further, additives may be incorporated as needed. Typical additivescommonly incorporated into polymer compositions for variousfunctionalities include catalysts or accelerators, surfactants, flameretardants, porosity control agents, antioxidants, colorants, pigments,fillers, and the like. Such additives will generally be incorporated inconventional amounts.

The thermoplastic resinous materials employed in one or more of the flowstream layers of the multilayer flow stream of the method of the presentinvention may optionally contain a blowing agent capable of providingexpanded compositions. That is, the multiple streams of thermoplasticresinous materials in the multilayer flow stream may independentlyprovide either expanded or non-expanded compositions. In an alternativeembodiment of the present invention, at least one stream includes ablowing agent to provide an expanded composition. As generally wellknown in the art, expanded compositions include a blowing, expansion orfoaming agent. Moreover, expanded thermoplastic resinous compositionscan incorporate one or more compositions yielding desiredfunctionalities such as a gas barrier (e.g. oxygen, carbon dioxide,etc.) composition (e.g., a film composition of ethylene vinyl alcoholcopolymer or polyvinylidene chloride), a liquid or moisture barriercomposition that substantially operates to prevent the liquid ormoisture from crossing from one side of the layer to the other side ofthe layer, a chemical barrier composition that substantially operates toprevent chemicals or gas from crossing from one side of the layer to theother side of the layer, an oxygen scavenger formulation, etc.

The multilayer annular structure comprising an expanded or foamed layermay be rigid or flexible, and includes blown and cast films, tubing,wire coating, fibers, and other shapes with annular profiles.

The multilayer structures can include recycled materials, if desired.For example, in blow molding applications, the trim-offs from the blowmolding operation can be used as a layer in the overall structure. Thistrim-off material includes all of the resins used in the multilayerstructure. For complex parts, the recycling can amount up to 50% of thetotal structure. The recycled material could be used as one of morelayers in the microlayer structure, it could be positioned between themicrolayer structure and any skin layer, or it could be used as the skinlayer. However, the use of the recycled material as skin layer may beless desirable due to the presence of the combination of differentresins which may interfere with the content to be packed if it is on theinside or with post printing steps if it is on the outside.

Materials for Alternative Embodiments Including Expanded Resinous Layers

In alternative embodiments employing expanded resinous layers, anythermoplastic resinous material either filled or unfilled with inorganicmaterial which can be blown or foamed may be employed for the layers ofthe present invention. These include and preferably are thethermoplastic resinous materials discussed above relating to thenon-expanded layers, including their relative preferences. In oneembodiment of the present invention, the same polymeric material can beemployed for each purpose, e.g., polystyrene can be employed as both anexpandable polymer resinous composition and as a non-expandablefilm-forming resinous composition in the same multilayer film compositestructure.

Substantially any of the known foaming, blowing, or expansion agents maybe incorporated into any one of or multiple thermoplastic resinousmaterials before the co-extrusion process. The blowing or expansionagents include, without limitation, physical blowing agents includinggaseous materials and volatile liquids and chemical agents whichdecompose into a gas and other byproducts. Representative blowing orexpansion agents include, without limitation, nitrogen, carbon dioxide,air, methyl chloride, ethyl chloride, pentane, isopentane,perfluoromethane, chlorotrifluoromethane, dichlorodifluoromethane,trichlorofluoromethane, perfluoroethane, 1-chloro-1,1-difluoroethane,chloropentafluoroethane, dichlorotetrafluoroethane,trichlorotrifluoroethane, perfluoropropane, chloroheptafluoropropane,dichlorohexafluoropropane, perfluorobutane, chlorononafluorobutane,perfluorocyclobutane, azodicarbonamide, azodiisobutyronitrile,benzenesulfonhydrazide, 4,4-oxybenzene sulfonyl-semicarbazide, p-toluenesulfonyl semicarbazide, barium azodicarboxylate, N,N′dimethyl-N,N′-dinitrosoterephthalamide, and trihydrazino triazine.

Chemical blowing agents include sodium bicarbonate, ammonium carbonateand ammonium hydrogencarbonate, citric acid or citrates, such as sodiumcitrate, sodium glutaminate, phthalic anhydride, benzoic acid,benzoates, such as aluminum benzoate, azodicarbonamide,azoisobutyronitrile and dinitropentamethylene. A preferred chemicalblowing agent comprises mixtures of sodium bicarbonate and citric acid,including Foamazol 72 brand CBA which is a concentrate containing amixture of citric acid and sodium bicarbonate in a pellet formcommercially available from Bergen International.

The blowing agent is generally employed in amounts as may be needed toprovide the desired amount of density reduction in the foam layer and inthe final article. The term “density reduction” and the densityreduction percentage mean the percentage the density is reduced in thefoam layer and/or the final article by using chemical and/or physicalblowing agent. For example, from a starting polymer (solid sheet)density of 1 g/cc, reduction of density to 0.9 g/cc is a 10% densityreduction, to 0.85 g/cc is a 15% density reduction, etc. In order tohave a combination of cost effectiveness and article performance, thefoamed thermoplastic polymer layer desirably has a density reduction ofat least about 10 weight percent (“wt %”) based on startingthermoplastic polymer density, preferably at least about 15 wt %, mostpreferably at least about 20 wt %. In order to maintain final productperformance properties such as thermoformability, the foamedthermoplastic polymer layer desirably has a density reduction of no morethan about 90 weight percent (“wt %”) based on starting thermoplasticpolymer density, preferably up to about 80 wt %, more preferably up toabout 70 wt %, most preferably up to about 60 wt %. In an alternativeembodiment, these density reduction ranges and levels can be provided inthe final multilayer structure by achieving an appropriate but somewhatgreater degree of density reduction in the expanded layer as needed forthe final product structure and desired density reduction.

The amount by weight of active chemical blowing agent incorporated intothe foamable composition to provide a desired level of density reductionis dependent upon the efficiency and effectiveness of the particularblowing agent but it is generally added in amounts of at least about0.016, preferably at least about 0.02 and more preferably at least about0.16 weight percent based on the total weight of chemical blowing agentactive ingredient, and up to amounts of about 0.8, preferably 0.4, andmore preferably 0.36 weight percent based on the total weight ofchemical blowing agent active ingredient and foamable polymercomposition.

With regard to the use of gas-generating liquid or other physicalblowing agent in a foam extrusion process, the added amount of physicalblowing agent incorporated into the foamable composition depends uponthe desired level of density reduction and the efficiency andeffectiveness of the particular blowing agent but it has been found tobe suitable to employ amounts of at least about 0.0001, preferably atleast about 0.001, more preferably at least about 0.01 and morepreferably at least about 0.063 weight percent based on the total weightof physical blowing agent and up to amounts of about 0.7 weight percent,preferably up to about 0.3, more preferably up to about 0.2 and mostpreferably up to about 0.128 weight percent based on the total weight ofphysical blowing agent.

Cell sizes and cell orientation for the expanded layers can be adjustedby known techniques to fall within desired or acceptable ranges asappropriate for the desired properties, and density reduction andexpanded layer thicknesses. See for example U.S. Pat. No. 5,215,691 andWO 2008/008875 which disclose forming flat multi-layered structureshaving expanded layers, and are both incorporated herein by reference.

The blowing agent must be incorporated into the expanded thermoplasticresinous material melt stream under a pressure which is sufficient toinhibit foaming of the melt stream until the stream is expressed throughthe co-extrusion die. Generally, this pressure should be at least 500psig and is preferably at least 1000 psig. Further, appropriateprocessing conditions are chosen to ensure that the blowing or expansionagent is sufficiently mixed and dissolved in the expandablethermoplastic resinous composition. For example, the melting temperatureof the non-expanded thermoplastic material may be lower than the desiredfoaming temperature for the expandable thermoplastic material, asdescribed in U.S. Pat. No. 5,215,691, incorporated herein by referencewith regard to provision of the expandable and expanded layers.

Preferably, the thermoplastic resinous materials and blowing or foamingagents for these layers are chosen to exhibit optimal properties in theresulting multilayer structure for the given application. In preferredembodiments, thermoplastic resinous materials are selected based onproperties desired in the final resulting structure as discussed above.

Preferably, in these alternative embodiments of the annular multilayerstructure comprising and expanded layer, the layers alternate betweenexpanded and non-expanded layers.

These foam layers including an expanded thermoplastic resinous materialare typically to provide a thickness of at least about 10 micrometers,preferably at least about 50 micrometers and more preferably at leastabout 75 micrometers. The thickness may be less than about 1,000micrometers, preferably less than about 500 micrometers and morepreferably less than about 300 micrometers. In a preferred embodiment,the density of each foam layer is in the range of about 0.03 to about0.8, preferably in the range of about 0.10 to about 0.5, grams per cubiccentimeter (g/cc) as may be measured by ASTM D 3575-93 W-B. In analternative embodiment, the density of the annular multilayer structurehaving been expanded layer may be in the range from about 0.05 to about0.9, preferably in the range of about 0.15 to about 0.6 g/cc.

The multilayer annular die products and process according to the presentinvention can advantageously be applied in the area of barrier packagingsuch as processed meat packaging. The currently used packaging materialsfor hotdogs, luncheon meats, and other processed meats typically havefrom 7 to 11 layers. A suitable 7 layer blown film structure of thistype (which can be subsequently thermoformed to form a bottom web) canbe prepared to a structure thickness of about four mills as follows:

Layer % mils Nylon 6 12 0.5 MAH-g-PE* 26 1.0 Nylon 6 5 0.2 EVOH (38 mol% ethylene) 10 0.4 Nylon 6 5 0.2 MAH-g-PE* 8 0.3 LLDPE 34 1.3 100 ~4.0*Maleic anhydride grafted polyethylene.

As known in the industry, decreasing levels of mol % ethylene of a EVOHresin typically increases barrier properties at the expense of toughnessand thermoformability. The forming web for these structures can range inthickness from 100-150 micrometers (4 to 6 mils). Problems withdowngaging of these existing multilayer barrier structures include lossof barrier due to poor thermoformability and/or rupture of the EVOH, andbalancing the barrier properties with toughness, optics, and filmeconomics.

The microlayer blown film process of the current invention offersgreater flexibility in achieving a larger number of layers (beyond 15and preferably beyond 27 layers) to optimize the structure to improve atleast one of the critical performance properties or a better balance ofthe key performance properties of toughness, barrier andthermoformability, and overall lower film cost or better film economics.

For example, a downgaged multi-layer barrier structure is as follows:

Layer % mils Nylon 6 13 0.4 Nylon tie 23 0.7 Nylon6/EVOH/Nylon 6(microlayer) 20 0.6 Nylon tie 10 0.3 LLDPE 34 1. 100  3

The reference to microlayer in the above structure and those that followrefers to composite multilayer structures of the present inventionwhereby the structure is comprised of alternating layers of thedisclosed polymer(s) having greater than 10 layers, more preferredgreater than 15 layers, and most preferred greater than 27 layers. Thesestructures may also include encapsulation of the microlayer compositestructure as described in the present invention.

A portion of the film is made up of microlayers of Nylon6/EVOH/Nylon6 oralternating microlayers of Nylon6 and EVOH. This structure offers adesired combination of barrier, toughness, thermoformability, and filmeconomics.

Alternately the Nylon/EVOH/Nylon center component of the original 4 milfilm structure could be replaced with a microlayered center component ofthe same total volume percentage of material, with the only change beingan increase in the total number of layers of each component, ultimatelyoffering increased barrier/shelf life and toughness for the application.

Another alternative example for a microlayer barrier structure follows:

Layer % mils PP/Versify microlayer 13 0.4 Nylon tie 23 0.7Nylon6/EVOH/Nylon 6 microlayer 20 0.6 Nylon tie 10 0.3 LLDPE 34 1.0 1003 *VERSIFY ™ is a propylene-ethylene elastomer or plastomer resin,available from The Dow Chemical Company.

Maleic anhydride (MAH) grafted ethylene copolymers can also be used as atie layer to EVOH in place of the Nylon 6 in the structure. Thisstructure could be made as a 3 or 4 mil film, depending on the toughnessrequired, to optimize cost performance balance. The microlayers ofpolypropylene (PP) and Versify improve the formability and toughnessversus a straight PP, to allow replacement of the more expensive Nylon.

The multilayer annular structure products and process according to analternative embodiment of the present invention can also advantageouslybe applied to provide film barrier improvement. Nylon MXD6 barrier isknown to improve via post fabrication orientation steps such astentering or double-bubble processes. This high barrier is desirablewhen preparing long shelf life, retort packages, where the food isexposed to high humidity during the retort process. However, theadditional orientation step via tentering adds significant cost. Theannular microlayer process of the present invention, can provide verythin layers of MXD6 emerging from a single manifold and can besubsequently oriented further in a blown film process. This offers acost effective barrier performance without the need to tenter(semi-solid orientation) the film. Blends of Nylon 6 or PET with nylonMXD6 can also be used in such microlayer structures, providing theoxygen barrier function in a final film.

In another alternative embodiment, the multilayer annular structureproducts and annular die process according to the present invention canadvantageously be applied in the area of film structures for dry foodpackaging. Dry food packaging includes applications such as cereal,crackers, cookies, and other moisture sensitive products. Thesestructures incorporate barrier materials for barrier to moisture,oxygen, and/or flavor and aroma. A typical multilayer package formoisture sensitive applications comprises a high-density polyethylene(HDPE) layer which can be used with Nylon or EVOH barrier layers,including tie layers and sealant layers, to provide the required barrierproperties for the given application. Although the thickness of thebarrier layer (e.g. EVOH or Nylon) can be increased to improve thebarrier, it is generally not accepted as an economical solution due tothe cost of the barrier resins or machinability issues that occur withthicker structures.

Thus, in alternative embodiments, the present invention can be veryadvantageously employed to provide microlayer barrier layer structure inannular multilayer structures, particularly in a blown film, to achievea larger number of thinner barrier layers, particularly beyond about 15and preferably beyond about 27 layers, to optimize the structure toimprove at least one of the critical performance properties or obtain abetter balance of the key performance properties, including but notlimited to, toughness, barrier, and optics, potentially also at overalllower cost if electing to downgauge.

Typical film structures are described below:

Layer Weight percent Sealant 15 HDPE 85

Layer Weight percent HDPE 55 Tie 10 NYLON 10 Tie 10 Sealant 15

Microlayered structures can be made according to alternative embodimentsof the present invention to achieve this balance using microlayers ofthe HDPE layer alone with a sealant layer, sealant layers typicallybeing made from many known polymers including but not limited to LLDPE,PB, EVA, or propylene plastomers and elastomers. Though not bound by thetheory, it has been postulated that a unique crystalline morphology thatimproves barrier property is produced in the very thin layers bymicrolayering. (Science, 223, pp 725-726, (2009)).

The proposed structures would be similar to those described above:

Layer Weight percent Sealant 15 Microlayered HDPE 85

Layer Weight percent HDPE 55 Microlayered Tie/NYLON/Tie 30 Sealant 15

Alternatively, the toughness could be enhanced by using a medium densitypolyethylene (MDPE) in place of the HDPE in the aforementioned examples.Also, to provide additional, better barrier and the ability to extendthe shelf life of dry foods, since water absorption leads to a decreasein flavor appeal, Nylon could be replaced with EVOH in the abovemicrolayered structure.

Another structure which can bring an improved combination of toughnessand barrier incorporates two microlayered composite structures withinthe total film structure.

Layer Weight percent Microlayered HDPE 55 Microlayered Tie/NYLON/Tie 30Sealant 15Another alternative embodiment structure is achieved by eliminating tielayers and offers an improved cost/performance balance:

Layer Weight percent Microlayer HDPE/NYLON 85 Sealant 15

Currently, when a multilayer film incorporating a barrier layer such asEVOH, HDPE, Nylon MXD6 or Nylon is recycled, the resulting polymer blendis simply used as filler, as it adds no additional barrier enhancementto the structure. The recycled barrier film can be incorporated into theblown microlayer structure, having very thin layers, for further barrierenhancement. This can result in longer shelf life or allow improvedeconomics via downgauging the barrier layer in the multilayer structure.

In another alternative embodiment, the multilayer annular die productsand process according to the present invention can advantageously beapplied in the area of nano clay barrier improvement. Researchers havetried to use nano clays or other inorganic fillers with polymers toimprove barriers to oxygen and moisture. However, these technologieshave not been cost effective and consistent. Microlayer blown filmsusing nano-clays or other inorganic fillers such as talcs, incombination with suitable thermoplastic polymer(s), enable improvementin barrier to gas molecule transport and provide a balance of toughnessand barrier properties. This enables improvements in silage wrap, heavyduty shipping sacks (HDSS), blister packaging, and other applicationsrequiring high resistance to gas molecule transport.

In another alternative embodiment, the multilayer annular die productsand process according to the present invention can advantageously beapplied in the area of heavy duty shipping sacks (HDSS). HDSS are usedto package items such as pet food, cement, mulch, fertilizer, andpolymer pellets. Typically multi-layer structures based on linear lowdensity polyethylene (LLDPE) or medium density polyethylene (MDPE) andpolypropylene is used. Typical structures include a three-layerstructure of LLDPE/PP/LLDPE (40/20/40) at 3 to 5 mil thickness. Thereremains a desire to improve the stiffness/toughness balance of the film.Microlayer structures enable desired improvements in stiffness/toughnessbalance and can further enable downgauging.

An example of a downgaged microlayer barrier HDSS structure comprisingmicro-layer core layer to provide the desired improvement instiffness/toughness balance is as follows:

Polymer Volume % LLDPE 30 LLDPE/PP microlayer 40 LLDPE 30

Collation shrink films are typically composed of LDPE and LDPE/LLDPEblends and multi-layer structures. Performance targets include goodoptics (low haze), high shrinkage and high shrink tension for obtaininga tight package, good puncture resistance and a high modulus. Forexample, films on the order of 2.25 mil (62 microns) thick are used forshrink wrapping of 24 packs of water or carbonated beverage. A typicalexample co-extruded structure is LLDPE/LDPE/LLDPE (10/80/10 volumepercent). The LLDPE skins are added to improve the toughness while theLDPE provides the shrink tension and optics. However, the balance in theabove properties is difficult to achieve with a single resin ormulti-layer structure.

In an alternative embodiment of the present invention, a microlayeredcore of LDPE, for example greater than 27 layers, could be provided toimprove the toughness without compromising the optics or shrink tension.In another embodiment, a microlayered LDPE/LLDPE core, having greaterthan 27 layers, can be used. Alternatively, a microlayered (preferablygreater than 27 layers) LDPE/LLDPE blend core can be used.

In an alternative embodiment of the present invention, the multilayerannular structures and processes for their production can be employed inproduction of blown stretch films. Stretch films are known to be used towrap large pallets and are applied either via machines or via handwrapping. Pallet wrap stretch film is applied on heavy loads typicallyby a wrapping machine equipped with stretching rollers. These stretchfilms are typically applied in a spiral, up and down wrapping processafter having stretched in the 100-300% stretch range. Hand wrap istypically applied by hand and the stretch ratio is not higher that 100%.Goods wrapped are generally any industrial products shipped by pallet,i.e. chemicals, plastics, boxes, household appliances, etc. The keyperformance properties for these types of stretch films are highextension at break, puncture resistance, and elmendorf tear resistance.Although these mechanical properties can be used to gauge performance,ultimate performance in use is evaluated using a lab scale stretchwrapping device such as supplied by Highlight Industries. This methodallows the determination of ultimate stretch, stretch force, unwindforce, and pallet wrap to get cling and puncture. Films are typically onthe order of about 20 micrometers (0.8 mils) in gauge. Additionally, thefilm usually has a cling layer for imparting cling. Typically, very lowdensity polyethylene (VLDPE), EVA, LLDPE, LLDPE/LDPE blends,polyisobutylene (PIB), polyolefin plastomers and elastomers, and blendsthereof are used in a cling layer. In addition, stretch films may alsohave a release layer with typical release layer materials including:MDPE, LLDPE/LDPE blends, as well as propylene-based polymers includingrandom copolymers (RCP), and blends thereof.

A typical three layer blown stretch film structure (one-sided cling) is:

Polypropylene RCP (release layer)—0.1 mil

LLDPE (core layer)—0.6 mil

VLDPE (cling layer)—0.1 mil

According to alternative embodiments of the present invention, otherwisesimilar annular, blown one-sided cling film structures for stretch wrapapplication are provided with core layers of microlayer LLDPE ormicrolayer LLDPE A/LLDPE B, where LLDPE A and LLDPE B are two differentLLDPE resins. Microlayer core layer components using more than twoLLDPEs can also be used in the above structure. The above microlayercomposite film structures give desired combination of toughness,stretchability and holding force as compared to a typical multi-layerstructure, and also allowing for improved film economics via downgaging.Alternatively, LLDPE A/LLDPE B could be replaced with variouscombinations of LLDPE, LDPE, HDPE, and propylene based polymers andblends thereof.

In addition, in an alternative embodiment of the present invention, theLLDPE core layer in a typical three layer stretch film with two-sidedcling film properties could be replaced with a microlayer LLDPE corecomponent to provide a structure as follows:

LLDPE/VLDPE blend (cling layer)—0.1 mil

Microlayer LLDPE (core layer)—0.6 mil

LLDPE/VLDPE blend (cling layer)—0.1 mil

The above microlayer composite film structures give desired combinationsof toughness, stretchability and holding force as compared tonon-microlayer multi-layer structures, allowing for improved filmeconomics via downgaging.

The present invention is illustrated in further detail by the followingexamples. The examples are for the purposes of illustration only, andare not to be construed as limiting the scope of the present invention.

Example #1

A film having a thickness of about 50 micrometers and containing 31alternating layers of low density polyethylene is produced using a 178mm diameter annular die on a blown film line. This film is produced bymaking a multilayer flow stream which is a stack of 27 layers andencapsulating that stack with another polyethylene layer and thenfeeding that structure into the central distribution manifold of amultilayer stacked annular die. The multilayer flow stream structure isformed in a conventional feedblock fed by a 51 mm extruder and a 19 mmextruder, for example, generally according to the feedblock process asshown in U.S. Pat. No. 3,557,265 then multiplied by a multiplier step asshown by U.S. Pat. No. 5,094,793.

These layers are then encapsulated with another polyethylene layergenerally according to the process as shown in U.S. Pat. No. 6,685,872.The encapsulated flow stream has a generally rectangular cross sectionalgeometry, is transitioned to a circular transfer stream using a circularflow tube channel and delivered to the manifold of the planar annulardie having a modified crosshead geometry to provide an extrudedmultilayer annular structure having an overlap area. The multilayerstructure flows through the distribution manifold which forms an annularmultilayer structure and provides layer overlap in an area of theextruded annular structure as shown in U.S. Pat. No. 6,685,872. As alsoshown in U.S. Pat. No. 6,685,872, two additional polyethylene skins areapplied using separate distribution manifolds in the multilayer annulardie. The annular multilayer flow stream exits the annular die as anannular multilayer structure and is inflated at a blowup ratio of 2:1.The bubble is collapsed and split into two film webs. Films wereproduced at rates of 14 to 32 kg/hr. This process is outlined in FIG. 1.

Example #2

A 500 micrometer annular film/foam structure containing 31 layers withalternating layers of low density polyethylene foam and film is producedon a 178 mm diameter die on a blown film line. This film is produced bymaking a multilayer flow stream in the form of a stack of 27 layers (13expandable layers, 14 nonexpandable film layers) and encapsulating thatstack with another polyethylene layer as described above for Example 1.The encapsulated flow stream is then delivered through a transfer lineas described above for Example 1 to the annular die having a modifiedcrosshead geometry and extruded as described above for Example 1. Themultilayer structure flows through the center distribution manifoldforming an annular microlayer structure with a layer overlap area andhas polyethylene skins applied using separate distribution manifolds inthe multilayer annular die. The annular multilayer flow stream exits theannular die and is inflated at a blowup ratio of 2:1. The bubble iscollapsed and split into two film webs. Structures are produced at ratesof 14 to 32 kg/hr. The structure has a resulting density of about 0.5g/cc.

Example #3

A multilayer polyethylene blowmolded structure is prepared using aparison provided by a co-extrusion line that has two 19 mm diametersingle screw extruders that feed two components through gear pumps intoa feedblock generally according to U.S. Pat. No. 3,557,265 and series oflayer multipliers similar in design to those described in U.S. Pat. Nos.5,202,074 and 5,094,783. The multilayered polyethylene resin feedstreamis encapsulated, generally according to the technique shown in U.S. Pat.No. 6,685,872 to provide a multilayer feed stream and forwarded into anannular crosshead die having a diameter of 38 mm and combining the edgesof the split flow streams at the backside of the manifold (i.e., notproviding an overlap area in the extruded annular structure). Overallextrusion rate is varied between approximately 9 kg/h to 18 kg/h. Theannular extrudate is then captured in the cavity of a 350 ml cylindricalbottle mold, inflated, and cooled to form a part. These structures areformed on a 38 mm diameter die with a die lip gap of 1.52 mm. The partformation is completed in a 350 ml cylindrical mold with an inflationpressure of 0.4 MPa.

Example #4

A multilayer blow molded structure with alternating layers ofpolyethylene foam and film having different degrees of macro-cellularorientation are prepared from parisons prepared according to the processshown in Example 3 wherein one of the extruders provides a polyethylenecomponent that contains 2 weight percent of an azodicarbonamide chemicalfoaming agent. Overall extrusion rate is varied between approximately 9kg/h to 18 kg/h. The annular extrudate is then captured in the cavity ofa 350 ml cylindrical bottle mold, inflated with an inflation pressure of0.4 MPa, and cooled to form a part. These structures are formed on a 38mm diameter die with a die lip gap of 1.52 mm. The overall density ofthe bottle is approximately 0.5 g/cc.

Procedure

A film having a thickness of about 100 micrometers and containing 6single layers of LLDPE skins and tie layers, and 27 alternating layersof EVOH and tie layer using a 178 mm diameter annular die on a blownfilm line. This film is produced by making a core multilayer flow streamwhich is a stack of 13 EVOH and 14 tie layers, encapsulating that stackwith another tie layer, and then feeding that structure into the centraldistribution manifold of a multilayer stacked annular die. Themultilayer flow stream structure is formed in a conventional feedblockfed by a 44.45 mm extruder and a 38.1 mm extruder, for example,generally according to the feedblock process, as shown in U.S. Pat. No.3,557,265, then multiplied by a multiplier step, as shown by U.S. Pat.No. 5,094,793.

These layers are then encapsulated with another tie layer generallyaccording to the process as shown in U.S. Pat. No. 6,685,872. Theencapsulated flow stream has a generally rectangular cross sectionalgeometry, is transitioned to a circular transfer stream using a circularflow tube channel and delivered to the manifold of the planar annulardie having a modified crosshead geometry to provide an extrudedmultilayer annular structure having an overlap area. The multilayerstructure flows through the distribution manifold which forms an annularmultilayer structure and provides layer overlap in an area of theextruded annular structure as shown in U.S. Pat. No. 6,685,872. As alsoshown in U.S. Pat. No. 6,685,872, two additional polyethylene skins areapplied using separate distribution manifolds in the multilayer annulardie. The annular multilayer flow stream exits the annular die as anannular multilayer structure and is inflated at a blowup ratio ofapproximately 1.7:1. The bubble is collapsed and split into two filmwebs. Films were produced at rates of 55 kg/hr. This process is outlinedin FIG. 1.

The materials used in the following examples are shown in Table 1.

Comparative Example 5

The following comparative structure is made using a conventional 7 layerdie at a blow-up ratio (BUR) of 1.7, a total line rate of 120 lb/hr, andthe extrusion temperatures listed in Table 2.

layer % # Resin of total film layers DOWLEX ™ 2247G LLDPE 30 1 BYNEL3861 10 1 50% Bynel 3861/50% Bynel 3860 2.5 1 EVALCA H171B 9 1 50% Bynel3861/50% Bynel 3860 2.5 1 BYNEL 3861 10 1 DOWLEX ™ 2247G LLDPE 20 1DOWLEX ™ 2247GLLDPE 20 1 DOWLEX ™ 2247G LLDPE 16 1

This structure is 3.68 mils thick, with a oxygen transmission at 23 Cand 80% RH of 0.238 cc/100 in²/day/atm. This calculates to apermeability of 0.077 cc-mil/100 in²/day/atm, which is comparable toliterature values for H171B at 23c and 80% RH.

Example 5

The following inventive example is produced on equipment as described inComparative Example 5. It uses the same H171B as the comparativeexample, but the H171B is microlayered with the tie layer to make a coreof 27 layers. The extrusion conditions are comparable to the control andlisted in Table 2. The structure is as follows:

layer % of # total film layers 58% DOWLEX ™ 2045.11G/42% ELITE ™ 30 15230GELITE 5230 58% DOWLEX ™ 2045.11G/42% ELITE ™ 5230G 10 1 Lotryl EMA29MA03 2.5 1 5% EVALCA H171B microlayered with 10% blend 15 27 (50%bynel 3861/50% admer nf498Anf498A) Lotryl EMA 29MA03 2.5 1 58% DOWLEX ™2045.11G/42% ELITE ™ 20 1 5230G ELITE 5230 58% DOWLEX ™ 2045.11G/42%ELITE ™ 20 1 5230G ELITE 5230

This structure has the H171B and the BYNEL/ADMER tie layer microlayeredtogether at a 1:2 ratio to form a total core thickness of 15% of thestructure, with a total of 5% H171B in the film structure. This 3.36 milfilm has an oxygen transmission at 23 C and 80% RH of 0.19 cc/100in²/day/atm. This calculates to a permeability 0.031 cc-mil/100in²/day/atm. This is 60% reduction in oxygen transmission from thecontrol 7 layer structure.

Example 6

Another inventive example is made using the equipment described inExample 5 and the extrusion conditions of Table 2.

The microlayer structure is made using 10% H171B. This structure has theH171B and the BYNEL/ADMER tie layer microlayered together at a 1:2 ratioto form a total core thickness of 20% of the structure, with a total of10% H171B in the film structure.

Layer % of # total film layers 58% DOWLEX ™ 2045.11G/42% ELITE ™ 30 15230GELITE 5230 EVA 3170 10 1 Lotryl EMA 29MA03 2.5 1 10% EVALCA H171Bmicrolayered with 10% blend 20 27 (50% bynel 3861/admer nf498A) LotrylEMA 29MA03 2.5 1 Dupont EVA 3170 15 1 58% DOWLEX ™ 2045.11G/42% ELITE ™20 1 5230GELITE 5230

This microlayered film has a thickness of 3.59 mils, with an oxygentransmission at 23 C and 80% RH of 0.29 cc/100 in²/day/atm. Thiscalculates to a permeability of 0.104 cc-mil/100 in²/day/atm.

These data show that Example 5, a 3.36 mil film with only 5% H171B, hasa lower oxygen transmission than either Comparative Example 5 or this10% H171B 27 layer core. This is due to the % H171B being divided intothinner layers, which optimized the crystallization and crystal size ofthe H171B, to reduce oxygen transmission.

Comparative Example #7

The same structure as made in Comparative Example 5 is tested for filmproperties.

This 3.7 mil multilayer film had a measured dart drop failure of 121grams, or 32.7 gm.mil (ASTM D1709). This sample had a MD Elmendorf tearof 24 gm/mil and an TD Elmendorf tear of 28 gm/mil (ASTM D1922).

Example 7

The following inventive example is produced on equipment as described inExample 5 and used the same H171B as the comparative example andmicrolayered the tie layer with it to make a core of 27 layers. Thesample is made at the conditions of Table 2. The structure is asfollows:

Layer % of total # film layers DOWLEX ™ Dow 2247G LLDPE 30 1 DOWLEX ™2247G LLDPE 10 1 50% BYNEL 3861/50% BYNEL 3860 2.5 1 5% EVALCA H171Bmicrolayered with 10% bynel 3861 15 27 50% BYNEL 3861/50% BYNEL 3860 2.51 DOWLEX ™ 2247G LLDPE2247G 20 1 DOWLEX ™ 2247G LLDPE2247G 20 1

This structure has the H171B and the BYNEL tie layer, microlayeredtogether at a 1:2 ratio to form a total core thickness of 15% of thestructure with a total of 5% H171B. The measured dart drop for this 4.25mil film is 259 or 60.9 gm/mil (ASTM D1709). This sample has a MDElmendorf tear of 44.5 gm/mil and an TD Elmendorf tear of 50.4 gm/mil(ASTM D1922).

Another inventive microlayer structure is made on the equipment inExample 5 using a 10% H171B microlayer level. The sample is made usingthe conditions of Table 2.

# Layer % of total film layers DOWLEX ™ 2247G LLDPE 30 1 DOWLEX ™ 2247GLLDPE 10 1 50% BYNEL 3861/50% BYNEL 3860 2.5 1 10% EVALCA H171Bmicrolayered with 20 27 10% bynel 3861 50% BYNEL 3861/BYNEL 3860 2.5 1DOWLEX ™ 2247G LLDPE 20 1 DOWLEX ™ 2247G LLDPE 15 1

This 3.94 mil film has a measured dart drop of 189 gms, or 48 gm/mil(ASTM D1709). This sample has a MD Elmendorf tear of 19.8 gm/mil and anTD Elmendorf tear of 16.8 gm/mil (ASTM D1922).

A third film is made on the equipment in Example 5 with the conditionsof Table 2.

# Layer % of total film layers DOWLEX ™ 2247G LLDPE 30 1 DOWLEX ™ 2247GLLDPE 10 1 Lotryl 29MA03 2.5 1 5% EVALCA H171B microlayered with 15 2710% 29MA03 Lotryl EMA 29MA03 2.5 1 DOWLEX ™ 2247G LLDPE 20 1 DOWLEX ™2247G LLDPE 20 1

This 3.23 mil film has a measured dart drop of 370 gm or 114.5 gm/mil(ASTM D1709). This sample has a MD Elmendorf tear of 97 gm/mil and an TDElmendorf tear of 259 gm/mil (ASTM D1922).

The two microlayered structures with 5% H171 divided into thin layersshow that toughness can be increased through optimizing the individuallayer thickness to control crystallization. The 10% EVOH, which wouldhave thicker individual layers, showed a lower toughness vs the 5%levels.

TABLE 1 Melt Flow (190 C./ Density (g/cc) 2.16 kg) ASTM D792 or ResinSupplier ASTM D1238 ISO 1183 % Comonomer DOWLEX ™ Dow Chemical 2.0 0.9172247G DOWLEX ™ Dow Chemical 1.0 0.922 2045.11G ELITE ™ Dow Chemical 4.00.916 5230 Bynel 3861 Dupont 2.0 0.95 Anhydride grafted ethylene vinylacetate Bynel 3860 Dupont 5.7 0.96 Anhydride grafted ethylene vinylacetate EVALCA Kuraray 1.7 1.17 Ethylene vinyl H171B alcohol (38 mol %ethylene) Lotryl EMA Arkema 2.0-3.5 — Ethylene methyl 29MA03 acrylate(27-31% MA) Admer nf498A Mitsui 3.0 0.910 per Modified ASMT D1505polyolefin Elvax 3170 Dupont 2.5 0.94 Ethylene vinyl acetate (18% VA)

TABLE 2 Extrusion Conditions Extruder 1 2 3 4 5 6 7 Skin Tie Barrier TieSkin Skin encapsulation Size inches 1.75 1.5 1.75 1.5 1.75 1.75 1.25Zone 1 380 380 380 380 380 380 350 Zone 2 400 400 400 400 400 400 400Zone 3 420 420 420 420 420 420 420 Zone 4 420 420 420 420 Die Adapter420 420 420 420 420 420 420 Screen 420 420 420 420 420 420 420 changerflange 420 420 420 420 420 420 420 Die 420 420 420 420 420 420 420

What is claimed is:
 1. A method of making an annular multilayerstructure, comprising: providing a multilayer flow stream ofthermoplastic resinous materials, the multilayer flow stream comprisinga microlayer portion having at least 30 layers and at least oneadditional layer on a first and second side of the microlayer portion,the microlayer portion having a microlayer structure; feeding themultilayer flow stream through a tubular flow channel having an inletand outlet to a single distribution manifold of an annular die, whereinthe tubular flow channel has a curved arc section between the inlet andoutlet, the curved arc section having a circular channel diameter,wherein the curved arc section has a radius of curvature larger than thecircular channel diameter; splitting the multilayer flow stream into atleast two flow streams, wherein the at least two flow streams move inopposite directions around a circumference of the distribution manifoldto form an annular multilayer flow stream, an end of one of the flowstreams overlapping an end of another flow stream in an overlapped area,and wherein the microlayer structure is maintained in the overlappedarea; and removing the annular multilayer flow stream from the annulardie to form the annular multilayer structure.
 2. The method of claim 1wherein providing the multilayer flow stream of thermoplastic resinousmaterials comprises: providing the microlayer portion; and encapsulatingthe microlayer portion with at least one encapsulating layer to form themultilayer flow stream.
 3. The method of claim 2 wherein providing themicrolayer portion comprises: providing a first flow stream having atleast two layers; splitting the first flow stream into at least twosubstreams; and joining the at least two substreams so that the firstsubstream is positioned on top of the second substream to form themicrolayer portion.
 4. The method of claim 1, wherein the distributionmanifold has a modified cross-head style geometry.
 5. The method ofclaim 1 wherein the distribution manifold has a planar geometry.
 6. Themethod of claim 1, wherein the distribution manifold has a cylindricalbody, a tapered cylindrical body or a planar body.
 7. The method ofclaim 1, further comprising providing at least one additional flowstream to the multilayer flow stream within the annular die using atleast one additional distribution manifold.
 8. The method of claim 7,wherein the at least one additional flow stream is a multilayer flowstream.
 9. The method of claim 1, further comprising adding a foamingagent or an inorganic filler material to at least one of thethermoplastic resinous materials before providing the multilayer flowstream.
 10. The method of claim 1, further comprising: placing theannular multilayer structure in the form of a parison inside a blowmolding mold and inflating the annular multilayer structure to the shapeof the mold.
 11. The method of claim 1, further comprising: drawing theannular multilayer structure in a molten state to bi-axially orient thestructure; and cooling the structure.
 12. The method of claim 11comprising: re-heating the cooled structure to a temperature below themelting point of the highest melting point polymer in the structure;drawing the structure uni-axially or bi-axially to orient the structure;and subsequently cooling the structure.
 13. An apparatus, comprising: afeedblock, with an optional layer multiplier, capable of providing amultilayer flow stream comprising a microlayer portion having at least30 layers and at least one additional layer on a first and second sideof the microlayer portion to a distribution manifold of an annular die;a tubular flow channel having an inlet and outlet, wherein the tubularflow channel has a curved arc section between the inlet and outlet, thecurved arc section having a circular channel diameter, and the curvedarc section has a radius of curvature larger than the circular channeldiameter, the tubular flow channel changing a direction of themultilayer flow stream while maintaining a microlayer structure of themicrolayer portion; and the annular die having at least one distributionmanifold that extrudes a multilayer flow stream, the distributionmanifold having an overlap area, the overlap area maintaining themicrolayer structure.
 14. The apparatus of claim 13, wherein thedistribution manifold has a modified crosshead style geometry.
 15. Theapparatus of claim 13 wherein the distribution manifold has a planargeometry.
 16. The apparatus of claim 13, further comprising anencapsulation die between the feedblock and the manifold thatencapsulates the multilayer flow stream prior to entry into thedistribution manifold.
 17. The apparatus of claim 13, wherein thetubular flow channel is positioned between the encapsulation die and thedistribution manifold and wherein the inlet of the tubular flow channelis oriented at about a 90 degree angle with respect to the outlet of thetubular flow channel.
 18. The apparatus of claim 13 wherein the tubularflow channel is positioned in the annular die.
 19. The apparatus ofclaim 13 wherein the tubular flow channel is positioned before theannular die.
 20. The apparatus of claim 13, wherein the distributionmanifold has a cylindrical body, a tapered cylindrical body or a planarbody.
 21. The method of claim 1 wherein a ratio of the radius ofcurvature of the curved arc section of the circular channel diameter isgreater than 3 to 1.